1. Field of the Technology
The present application relates generally to mobile stations operating in wireless communication networks, and more particularly to methods and apparatus for controlling the gain states of a wireless receiver operating in idle mode.
2. Description of the Related Art
A wireless communication device, such as a mobile station operating in a wireless communication network, may provide for both voice telephony and packet data communications. A mobile station may, for example, be compatible with 3rd Generation (3G) communication standards (such as UMTS), or utilize Global System for Mobile Communications (GSM), Time Division Multiple Access (TDMA), or Code Division Multiple Access (CDMA) wireless network technologies.
All of these communication standards utilize radio frequency (RF) signal detection techniques implemented in a RF receiver. A RF receiver may generally face three performance limiting factors: internal thermal noise, external in-band noise, and out-of-band interference. When internal thermal noise is the predominate source of interference to the desired signal, a low receiver noise figure is desired to improve receiver sensitivity. External in-band interference (including external in-band noise) can also be the major source of interference; especially when the out-of-band portion of the interference does not cause significant distortion. In this case, a higher in-band dynamic range of the receiver is desired for good performance. The in-band dynamic range of the receiver is usually measured by the in-band 3rd order interception point (i.e. “in-band IP3”). Finally, out-of-band interference may also result in distortions in the in-band spectrum through receiver non-linearities. In this case, a higher out-of-band dynamic range of the receiver is desired to improve performance. The out-of-band dynamic range is usually measured by the out-of-band 3rd order interception point (i.e. “out-of-band IP3”).
The aforementioned higher input dynamic range and lower noise figure may be contradictory requirements since higher input dynamic range means lower front end gain while lower noise figure suggests a higher front end gain design. A front end that is designed to satisfy both scenarios could be relatively expensive in cost. For a lower cost solution, some receiver designs include a variable front end stage. In particular, a low noise amplifier (LNA) in the front end may have an adjustable gain G, which is controlled by a feedback mechanism. In such a configuration, the gain G of the LNA can be adjusted dynamically in response to the feedback mechanism in order to trade off the noise figure with the dynamic range of the LNA when necessary.
To achieve the tradeoff, some feedback mechanisms include a level detector and a front end gain controller. The level detector receives an input signal and provides a signal level or received signal strength indicator (RSSI), and the front end gain controller receives this indicator to generate a control signal for controlling the front end gain.
In some configurations, the above feedback mechanism in a wireless receiver is used not only for continuous operation mode, but also for idle mode in a mobile station application. In idle mode, in order to save battery power, the receiver in a mobile station is turned off most of the time; it is periodically waken up at given time slots based on a predetermined schedule, such as every 1.28, 2.56 or 5.12 seconds, to receive message from base stations. A wake up period is usually very short in time, for example, about 100 ms in a CDMA2000™ mobile receiver. At the beginning of the wake up period, there is a warm-up period for settling the receiver to a steady state.